Load current dependent reduction of charge battery current

ABSTRACT

Circuits and methods to charge batteries of a portable device simultaneously with supplying power to the device for its operation, using a power source with limited maximum current, as e.g. an USB port, have been achieved. The system invented relies upon digital control only. No direct sensing of the current required for the operation of the portable device is required. The control takes care that the sum of the charging current and of the current to run the portable device does not exceed the maximum allowable current of the power source. The current required to run the portable device has precedence over the charging current.

This is a divisional application of U.S. patent application Ser. No.12/150,977 filed on May 2, 2008, which is herein incorporated byreference in its entirety, and assigned to a common assignee.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates generally to battery driven mobile devices andrelates more specifically to charging these mobile electronic devicesfrom power supplies providing only limited current as e.g. universalserial bus (USB) port.

(2) Description of the Prior Art

Battery driven portable electronic devices such as cellular telephones,personal digital assistants (PDAs), etc. are becoming very popular.

The batteries of the mobile have to be recharged periodically by anexternal power source, using a battery charger, usually receiving powerfrom a standard AC electrical outlet and converting the power into a lowDC voltage.

The charging of the batteries is often controlled by a battery chargecontroller to manage the charging of the battery. It is a challenge forthe designers of battery charge controllers when they are confrontedwith power supplies such as e.g. universal serial bus (USB) port havinga limited capacity only and if the power from such a supply is not onlyused for the charging of the batteries but also simultaneously for theoperation of the portable device.

The majority of personal computers (PCs) and laptop computers availabletoday are provided with one or more USB ports as standard components.Besides data communication USB ports can supply power to a connecteddevice in a limited extent. So called high-power USB ports can supply amaximum current of at least 500 mA and low-power USB ports can supply acurrent of usually 100 mA. Problems arise if the portable deviceconsumes at least temporarily most of the power delivered by an USBport, or by another source having limited current capacity, for its ownoperation and simultaneously the batteries need power for recharging. Anover current situation of such a power supply has to be avoided in anycase.

There are known patents or patent publications dealing with the chargingbatteries of portable devices via USB ports or the like:

U.S. Patent (U.S. Pat. No. 7,034,503 to Veselic et al.) proposes anintegral power node of a computer data bus, such as a USB (universalserial bus) port for a convenient source of charging power for portablecommunication devices. Unfortunately, USB ports have limited powercapacity, making them generally incompatible with battery chargecontrollers (BCCs) which are designed to receive a steady, high capacityinput. The invention provides a battery charging circuit, which adjuststo the parameters of an external power supply such as a USB port byadding a regulating circuit to a standard BCC design. This regulatingcircuit maximizes the current drawn by the BCC, while keeping thevoltage to the BCC above a preset minimum (the low voltage shut offlevel for the BCC). If the voltage to the BCC begins to drop, theregulating circuit reduces the current drawn, so the voltage rises andstays within the operating range of the BCC.

U.S. Patent (U.S. Pat. No. 6,946,817 to Fischer et al.) discloses asystem for powering and charging a mobile communication device includesa processing device, a rechargeable battery, a Universal Serial Bus(USB) interface, and a charging subsystem. The rechargeable battery isconfigured to supply power to the processing device. The USB interfaceis configured to connect to a USB port via a USB cable. The chargingsubsystem is coupled to the USB interface, and is configured to chargethe rechargeable battery using power received from the USB interface.

U.S. Patent application publication (US 2006/0244422 to DiGiovanna etal.) discloses methods and apparatus for charging a power sourcecomprising determining a type of power supply used by a base,communicating a charge rate to a power source charging module andproviding power to the power source at a charge rate. In one embodiment,a scanner can recharge from a cradle that receives power from either adedicated external power source or through USB by adjusting its chargerate based on a communication from the base.

Furthermore U.S. Patent (U.S. Pat. No. 6,507,172 to Sherman) disclosesan universal serial bus powered battery charger primarily intended foruse in battery powered hand-held and other portable devices to chargethe battery or batteries within the battery powered device when the sameis connected to a host device, powered hub or a bus powered hub througha universal serial bus (USB) port. The battery charger includes one ormore current limits to conform to the universal serial bus currentsupply limit set in the USB specification. Any of the universal serialbus voltage and current limits may be used to charge batteries in thebattery-powered device, such as single cell lithium-ion batteries.

SUMMARY OF THE INVENTION

A principal object of the present invention is to achieve methods andsystems to charge batteries of portable devices simultaneously withsupplying power to these devices for their operations from a powersupply having limited current capacity.

A further object of the present invention is to achieve a fully digitalcontrol of the systems invented.

A further object of the present invention is to avoid exceeding theallowable current limit of the power source used.

Another object of the present invention is to have precedence of thecurrent required to run the portable device over a charging current.

In accordance with the objects of this invention a method to chargebatteries of portable devices simultaneously with supplying power tothese devices for their operations has been achieved. The methodinvented comprises, first, step 1: providing a DC power source, a supplyregulator, one or more rechargeable batteries, a battery chargercontrolled by a digital control unit, a voltage comparator, and acapacitor, step 2: setting charge current to charge batteries to apredefined default current level, and step 3: delaying process flow fora defined time interval. The following steps include step 4: checking ifvoltage at inputs of said portable device and of said battery charger islower than a defined threshold voltage, and, if positive, go to step (5)else go to step (7), step 5: checking, if said charge current is zero,and if positive, go to step (3) else go to step (6), and step 6:decreasing said charge current and go then to step (3). The last stepscomprise step 7: checking if said charge current is smaller than saidpredefined default current level, and if positive, go to step (8), elsego to step (3), and step 8: increasing said charge current and go thento step (3).

In accordance with the objects of this invention a system to chargebatteries of a portable device simultaneously with supplying power tothe device for its operation has been achieved. The system inventedcomprises, first, a rechargeable battery, a DC power source connected atits output to a supply regulator, and said supply regulator regulatingits output voltage and limiting its output current just below themaximum allowable output current of said DC power supply, wherein theoutput of the supply regulator is supplying the operation of theportable device and its voltage corresponds to the supply voltage levelrequired the portable device, and the output is further connected to thepower input of a battery charger, charging said rechargeable battery, toa first terminal of a capacitor, and to a first input of a voltagecomparator. Furthermore the system comprises said capacitor having itssecond terminal connected to ground, said battery charger, charging withits output said rechargeable battery, having its operation controlled bya digital controller, said digital controller wherein an input isconnected to an output of said voltage comparator, and said voltagecomparator having a reference voltage as a second input comparing saidreference voltage with the output voltage of said supply regulator.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings forming a material part of thisdescription, there is shown:

FIG. 1 shows a schematic block diagram of a preferred embodiment of thepresent invention.

FIG. 2 illustrates a flowchart of the method invented to chargebatteries of portable devices simultaneously with supplying power tothese devices for their operations from a power supply having limitedcurrent capacity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments disclose methods and systems to chargebatteries of portable devices simultaneously with supplying power tothese devices for their operations from a power supply having limitedcurrent capacity as e.g. universal serial bus (USB) port. It is to beunderstood that the present invention can support more than oneseparated portable devices each having their own battery charge system.

An USB port provides usually either 100 mA or 500 mA, wherein USB portshaving even higher currents than 500 mA are available today. In case thesum of the charge current and the system current, i.e. the currentrequired for the operation of the portable device, exceeds the currentcapacity of the power supply, the output voltage to the portable devicestarts to drop and the operation of the portable device is in jeopardy.

The preferred embodiments of the present invention measure the systemcurrent and adjust (e.g. decrease) the charge current in a way that thesum of the two currents does not exceed the maximum allowable currentfrom the power supply. This approach gives priority to the systemcurrent over the charging current.

FIG. 1 shows a schematic block diagram of a preferred embodiment of thepresent invention. The system voltage node VSYSTEM, i.e. the voltage tosupply the operation of the portable device, is controlled by a supplyregulator 2; this can be e.g. a linear regulator (LDO) with a currentlimit or a switched regulator with current limit (buck, boost, buckboosttype). The voltage level of VSYSTEM is defined by the voltage levelrequired for the operation of the portable device. This supply regulator2 incorporates a current limiting circuitry having a current limit justbelow the maximum current of the current source 1, in a preferredembodiment an USB bus. It should be understood that the presentinvention is applicable to any other power supply having a maximumcurrent limit close to the current demand to charge and run the portabledevice simultaneously, e.g. a Firewire/IEEE1394 port, or a currentlimited wall brick). In a preferred embodiment all components 2-8, withthe exception of the power source 1, of the present invention areintegrated in the portable device, which is supported by the systeminvented. It is obvious that the present invention would be applicablefor embodiments wherein all or some of the components would not beintegrated into a device.

Furthermore there must be a system capacitance 4 present on the VSYSTEMnode for filtering and decoupling. For the capacitance required eitheran already existing capacitance of the system is (re-) used or a newcapacitor 4 is added. This system capacitance 4 establishes the relationbetween current and voltage, as the present invention acts on currentsas setting the current level for ICH but reacts on voltage as thecomparator 7, comparing VSYSTEM with Vtrip. The system node at thecapacitor establishes a summing point between incoming current (from theregulator) and outgoing current (ICH and ISYSTEM).

Current is delivered from the node VSYSTEM to the system load 3, i.e.the load of the operation of the portable device, and via charger 5 tothe battery 6 of the portable device when charging is performed. UsuallyLi-ion batteries are used for such applications. The battery might ormight not be removable.

When the sum of the system load current ISL and of the charging currentICH exceeds the current limit of the supply regulator 2, the voltage atthe VSYSTEM node starts to drop below its nominal voltage level becausethere is less current (it's limited) flowing into the capacitance thanis drawn out of the capacitance by ICH and ISYSTEM. At a definedthreshold voltage VTRIP, which is below the nominal voltage level ofVSYSTEM node, the comparator 8, comparing voltage level VSYSTEM with thethreshold voltage VTRIP, indicates the voltage drop of VSYSTEM nodevoltage to the digital control 8 of the charger 5. After receiving theindication of a voltage drop of voltage VSYSTEM below threshold voltageVTRIP, the digital control unit, controlling charger 5, decreases thecharge current ICH until voltage VSYSTEM comes back until a voltagelevel above threshold voltage VTRIP is reached. After the comparator 7indicates to the digital control unit 8 that VSYSTEM voltage is higherthan threshold voltage VTRIP, the digital control unit 8 is increasingcharge current ICH via charger 5 until the current limit of the supplyregulator 2 is reached and VSYSTEM run voltage falls again.

The periodic decrease/increase of the charge current ICH results inVSYSTEM voltage settling around the comparator threshold voltage VTRIPas long as the system current ISL does not exceed the current limit seton supply regulator 2. In this case the charge current ICH is alreadyreduced to zero and inevitably drops further. The intention of thepresent invention is that the system load current ISL gets precedenceover the charge current ICH.

FIG. 2 illustrates a flowchart of the method invented to chargebatteries of portable devices simultaneously with supplying power tothese devices for their operations from a power supply having limitedcurrent capacity.

Step 20 of FIG. 2 illustrates the start procedure, i.e. enabling thecharging. In the following step 21 the charging current ICH is set bydigital control unit 8 to a defined default level ICH _(—) DEF. Thedefined default level ICH _(—) DEF could be any current not exceedingthe maximum allowable charge current. The following step 22 comprises atime delay to stabilize the regulation of the charge current. Withouttime delay the charge current would be increased/decreased in one rushall the way up/down. By the delay this step-up/down behavior iscontrolled. Therefore the voltage at VSYSTEM settles smoothly in theequilibrium state, i.e. the incoming current corresponds to the outgoingcurrent at sum node. The delay can be in the order of magnitude ofbetween 1 us and couple 100 us. The delay is incorporated in the digitalcontrol and stabilizes the system.

Step 23 describes a check if the voltage level VSYSTEM is smaller thanthreshold voltage VTRIP. In a preferred embodiment this check isperformed by comparator 23, wherein the comparator produces an digitaloutput. Furthermore it should be noted that in a preferred embodimentall steps are performed digitally except the voltage comparison of step23.

In case VSYSTEM is equal to or higher than VTRIP the process flow goesto step 24. In a preferred embodiment the value of VTRIP is slightlylower than an nominal level of VSYSTEM.

Step 24 describes another check, namely if the actual charge current ICHis smaller than the defined default charge current ICH _(—) DEF. In caseof the actual charge current ICH being smaller than the default chargecurrent ICH _(—) DEF; the process flow goes to step 25, wherein theactual charge current ICH is increased. In a preferred embodiment thisincrease is controlled by digital control unit 8. Then the process flowgoes back to step 22.

In case the result of the check of step 24 is that ICH is not smallerthan the default charge current ICH _(—) DEF, the process flow goesdirect back to step 22. In a preferred embodiment the comparison betweenICH and ICH _(—) DEF is performed digitally. These are digital controlsettings (vectors) for the charge current. In case the check of step 23results in VSYSTEM being smaller than VTRIP the process flow goes tostep 26.

Step 26 describes another check, namely if the actual charge current ICHis zero. In case of the actual charge current ICH being not zero, theprocess flow goes to step 27, wherein the actual charge current ICH isdecreased. In a preferred embodiment this decrease is controlled bydigital control unit 8. Then the process flow goes back to step 22.

Summarizing the present invention it should be noted that importantpoints of the invention are that an indirect measurement of the systemload current is performed using a comparator and capacitor 4.

Therefore no direct sensing of the system load current ISL is required.Furthermore it should be noted that all control of the system inventedis performed digitally by digital control unit 8.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

1. A system to charge batteries of a portable device simultaneously withsupplying power to the device for its operation is comprising: arechargeable battery, a DC power source connected at its output to asupply regulator; said supply regulator regulating its output voltageand limiting its output current just below the maximum allowable outputcurrent of said DC power supply, wherein the output of the supplyregulator is supplying the operation of the portable device and itsvoltage corresponds to the supply voltage level required the portabledevice, and the output is further connected to the power input of abattery charger, charging said rechargeable battery, to a first terminalof a capacitor, and to a first input of a voltage comparator; saidcapacitor having its second terminal connected to ground; said batterycharger, charging with its output said rechargeable battery, having itsoperation controlled by a digital controller; said digital controllerwherein an input is connected to an output of said voltage comparatorand the output is connected to said battery charger; and said voltagecomparator having a reference voltage as a second input comparing saidreference voltage with the output voltage of said supply regulator. 2.The system of claim 1 wherein said DC power source has a maximumallowable current limit.
 3. The system of claim 2 wherein said DC powersource is a universal serial bus (USB) port.
 4. The system of claim 2wherein said DC power source is a Firewire/IEEE1394 port.
 5. The systemof claim 2 wherein said DC power source is a current limited wall brick.6. The system of claim 1 wherein said supply regulator, one or morerechargeable batteries, the battery charger, the digital control unit,the capacitor, and the voltage comparator are integrated in saidportable device.
 7. The system of claim 1 wherein a system capacitancereplaces said capacitor.
 8. The system of claim 1 wherein said supplyregulator allows a maximum output current, which is slightly lower thansaid maximum allowable current limit of said DC power source.
 9. Thesystem of claim 1 wherein said supply regulator is a linear regulator.10. The system of claim 1 wherein said supply regulator is a switchedregulator.
 11. The system of claim 1 wherein more than one rechargeablebattery is deployed.
 12. The system of claim 1 wherein said digitalcontrol controls the battery charger in a way that the current requiredfor the operation of the portable device has precedence over thecharging current of the batteries.